How to cut video with FFmpeg C API

Question

How can I cut video with FFmpeg C API? From 00:10:00 to 00:20:00 for example. What functions I need to use?

I convert video using this function:

int convert(char *file) {
    AVFrame *frame;
    AVPacket inPacket, outPacket;

    if(avio_open(&outFormatContext->pb, file, AVIO_FLAG_WRITE) < 0) {
        fprintf(stderr, "convert(): cannot open out file\n");
        return 0;
    }

    avformat_write_header(outFormatContext, NULL);
    frame = avcodec_alloc_frame();
    av_init_packet(&inPacket);

    while(av_read_frame(inFormatContext, &inPacket) >= 0) {
        if(inPacket.stream_index == inVideoStreamIndex) {
            avcodec_decode_video2(inCodecContext, frame, &frameFinished, &inPacket);
            if(frameFinished) {
                av_init_packet(&outPacket);
                avcodec_encode_video2(outCodecContext, &outPacket, frame, &outputed);
                if(outputed) {
                    if (av_write_frame(outFormatContext, &outPacket) != 0) {
                        fprintf(stderr, "convert(): error while writing video frame\n");
                        return 0;
                    }
                }
                av_free_packet(&outPacket);
            }
        }
    }

    av_write_trailer(outFormatContext);
    av_free_packet(&inPacket);
    return 1;
}

Answer 1

As Wagner Patriota says, "if you just wanna cut the video, you don't need to reencode the video if you want". Here is the code based on ffmpeg remuxing.c example that you don't need to reencode the video.

#include <libavutil/timestamp.h>
#include <libavformat/avformat.h>

static void log_packet(const AVFormatContext *fmt_ctx, const AVPacket *pkt, const char *tag)
{
    AVRational *time_base = &fmt_ctx->streams[pkt->stream_index]->time_base;

    printf("%s: pts:%s pts_time:%s dts:%s dts_time:%s duration:%s duration_time:%s stream_index:%d\n",
           tag,
           av_ts2str(pkt->pts), av_ts2timestr(pkt->pts, time_base),
           av_ts2str(pkt->dts), av_ts2timestr(pkt->dts, time_base),
           av_ts2str(pkt->duration), av_ts2timestr(pkt->duration, time_base),
           pkt->stream_index);
}

int cut_video(double from_seconds, double end_seconds, const char* in_filename, const char* out_filename) {
    AVOutputFormat *ofmt = NULL;
    AVFormatContext *ifmt_ctx = NULL, *ofmt_ctx = NULL;
    AVPacket pkt;
    int ret, i;

    av_register_all();

    if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, 0)) < 0) {
        fprintf(stderr, "Could not open input file '%s'", in_filename);
        goto end;
    }

    if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) {
        fprintf(stderr, "Failed to retrieve input stream information");
        goto end;
    }

    av_dump_format(ifmt_ctx, 0, in_filename, 0);

    avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, out_filename);
    if (!ofmt_ctx) {
        fprintf(stderr, "Could not create output context\n");
        ret = AVERROR_UNKNOWN;
        goto end;
    }

    ofmt = ofmt_ctx->oformat;

    for (i = 0; i < ifmt_ctx->nb_streams; i++) {
        AVStream *in_stream = ifmt_ctx->streams[i];
        AVStream *out_stream = avformat_new_stream(ofmt_ctx, in_stream->codec->codec);
        if (!out_stream) {
            fprintf(stderr, "Failed allocating output stream\n");
            ret = AVERROR_UNKNOWN;
            goto end;
        }

        ret = avcodec_copy_context(out_stream->codec, in_stream->codec);
        if (ret < 0) {
            fprintf(stderr, "Failed to copy context from input to output stream codec context\n");
            goto end;
        }
        out_stream->codec->codec_tag = 0;
        if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
            out_stream->codec->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
    }
    av_dump_format(ofmt_ctx, 0, out_filename, 1);

    if (!(ofmt->flags & AVFMT_NOFILE)) {
        ret = avio_open(&ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE);
        if (ret < 0) {
            fprintf(stderr, "Could not open output file '%s'", out_filename);
            goto end;
        }
    }

    ret = avformat_write_header(ofmt_ctx, NULL);
    if (ret < 0) {
        fprintf(stderr, "Error occurred when opening output file\n");
        goto end;
    }

    //    int indexs[8] = {0};


    //    int64_t start_from = 8*AV_TIME_BASE;
    ret = av_seek_frame(ifmt_ctx, -1, from_seconds*AV_TIME_BASE, AVSEEK_FLAG_ANY);
    if (ret < 0) {
        fprintf(stderr, "Error seek\n");
        goto end;
    }

    int64_t *dts_start_from = malloc(sizeof(int64_t) * ifmt_ctx->nb_streams);
    memset(dts_start_from, 0, sizeof(int64_t) * ifmt_ctx->nb_streams);
    int64_t *pts_start_from = malloc(sizeof(int64_t) * ifmt_ctx->nb_streams);
    memset(pts_start_from, 0, sizeof(int64_t) * ifmt_ctx->nb_streams);

    while (1) {
        AVStream *in_stream, *out_stream;

        ret = av_read_frame(ifmt_ctx, &pkt);
        if (ret < 0)
            break;

        in_stream  = ifmt_ctx->streams[pkt.stream_index];
        out_stream = ofmt_ctx->streams[pkt.stream_index];

        log_packet(ifmt_ctx, &pkt, "in");

        if (av_q2d(in_stream->time_base) * pkt.pts > end_seconds) {
            av_free_packet(&pkt);
            break;
        }

        if (dts_start_from[pkt.stream_index] == 0) {
            dts_start_from[pkt.stream_index] = pkt.dts;
            printf("dts_start_from: %s\n", av_ts2str(dts_start_from[pkt.stream_index]));
        }
        if (pts_start_from[pkt.stream_index] == 0) {
            pts_start_from[pkt.stream_index] = pkt.pts;
            printf("pts_start_from: %s\n", av_ts2str(pts_start_from[pkt.stream_index]));
        }

        /* copy packet */
        pkt.pts = av_rescale_q_rnd(pkt.pts - pts_start_from[pkt.stream_index], in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
        pkt.dts = av_rescale_q_rnd(pkt.dts - dts_start_from[pkt.stream_index], in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
        if (pkt.pts < 0) {
            pkt.pts = 0;
        }
        if (pkt.dts < 0) {
            pkt.dts = 0;
        }
        pkt.duration = (int)av_rescale_q((int64_t)pkt.duration, in_stream->time_base, out_stream->time_base);
        pkt.pos = -1;
        log_packet(ofmt_ctx, &pkt, "out");
        printf("\n");

        ret = av_interleaved_write_frame(ofmt_ctx, &pkt);
        if (ret < 0) {
            fprintf(stderr, "Error muxing packet\n");
            break;
        }
        av_free_packet(&pkt);
    }
    free(dts_start_from);
    free(pts_start_from);

    av_write_trailer(ofmt_ctx);
end:

    avformat_close_input(&ifmt_ctx);

    /* close output */
    if (ofmt_ctx && !(ofmt->flags & AVFMT_NOFILE))
        avio_closep(&ofmt_ctx->pb);
    avformat_free_context(ofmt_ctx);

    if (ret < 0 && ret != AVERROR_EOF) {
        fprintf(stderr, "Error occurred: %s\n", av_err2str(ret));
        return 1;
    }

    return 0;
}

Answer 2

If you just wanna cut the video, you don't need to reencode the video if you want. So I am supposing you wanna cut and reencode for some reason. So, based on your code:

Observe you must to have access to the video AVStream* structure... I named it as inVideoStream.

int convert_and_cut(char *file, float starttime, float endtime) {
    AVFrame *frame;
    AVPacket inPacket, outPacket;

    if(avio_open(&outFormatContext->pb, file, AVIO_FLAG_WRITE) < 0) {
        fprintf(stderr, "convert(): cannot open out file\n");
        return 0;
    }

    // seek to the start time you wish.
    // BEGIN
    AVRational default_timebase;
    default_timebase.num = 1;
    default_timebase.den = AV_TIME_BASE;

    // suppose you have access to the "inVideoStream" of course
    int64_t starttime_int64 = av_rescale_q((int64_t)( starttime * AV_TIME_BASE ), default_timebase, inVideoStream->time_base);
    int64_t endtime_int64 = av_rescale_q((int64_t)( endtime * AV_TIME_BASE ), default_timebase, inVideoStream->time_base);

    if(avformat_seek_file(inFormatContext, inVideoStreamIndex, INT64_MIN, starttime_int64, INT64_MAX, 0) < 0) {
        // error... do something...
        return 0; // usually 0 is used for success in C, but I am following your code.
    }

    avcodec_flush_buffers( inVideoStream->codec );
    // END

    avformat_write_header(outFormatContext, NULL);
    frame = avcodec_alloc_frame();
    av_init_packet(&inPacket);

    // you used avformat_seek_file() to seek CLOSE to the point you want... in order to give precision to your seek,
    // just go on reading the packets and checking the packets PTS (presentation timestamp) 
    while(av_read_frame(inFormatContext, &inPacket) >= 0) {
        if(inPacket.stream_index == inVideoStreamIndex) {
            avcodec_decode_video2(inCodecContext, frame, &frameFinished, &inPacket);
            // this line guarantees you are getting what you really want.
            if(frameFinished && frame->pkt_pts >= starttime_int64 && frame->pkt_pts <= endtime_int64) {
                av_init_packet(&outPacket);
                avcodec_encode_video2(outCodecContext, &outPacket, frame, &outputed);
                if(outputed) {
                    if (av_write_frame(outFormatContext, &outPacket) != 0) {
                        fprintf(stderr, "convert(): error while writing video frame\n");
                        return 0;
                    }
                }
                av_free_packet(&outPacket);
            }

            // exit the loop if you got the frames you want.
            if(frame->pkt_pts > endtime_int64) {
                break;
            }
        }
    }

    av_write_trailer(outFormatContext);
    av_free_packet(&inPacket);
    return 1;
}